SACRAMENTO – In a shot that no one seemed to see coming, least of all Joseph Benavivdez, Demetrious Johnson retained his flyweight title with a massive knockout on Saturday night in front of Benavidez’s hometown fans.

With Benavidez throwing a left, Johnson drilled him with a right hand on the button. Benavidez’s legs gave out and he hit the canvas. “Mighty Mouse” dropped four more fists on the challenger before the stoppage came at the 2:08 mark of the first round.

The flyweight title bout was the main event of today’s UFC on FOX 9 event at Sleep Train Arena in Sacramento. It aired on FOX following prelims on FOX Sports 1 and MMAjunkie.

Benavidez pushed forward early with kicks as Johnson danced on the outside. The challenger backed the champ up several times early with kicks, then tried to get inside with punches while changing his stance.

But as Johnson took the center of the cage and backed Benavidez up toward the fence, he then landed a bomb of a right hand that may have had Benavidez out before he even hit the canvas.

After referee John McCarthy pulled Johnson off, the champ did a backflip in the center of the octagon to celebrate. He became the first fighter to finish Benavidez – who now has four losses in his career, with two to Johnson and two to bantamweight champion Dominick Cruz.

Johnson defended his flyweight title for the third time. He won the belt 15 months ago with a split-decision win over Benavidez at UFC 152 in Toronto. Talk before the fight was that the rematch might prove to be much different with Benavidez training under new Team Alpha Male head coach Duane Ludwig. But this time around was clearly decisive – and not in the way some were expecting.

“Tonight was a great moment for my career, but in reality it’s just another fight,” Johnson said. “My goal is to keep evolving and displaying my skill set to fans and having them enjoy my fights.”

Benavidez was understandably disappointed, and now has lost all three of the title fights he’s been in – two to Johnson and a shot at the WEC bantamweight title against Cruz.

“I’m so upset right now – I thought tonight was going to be my night,” Benavidez said.

Johnson (19-2-1 MMA, 7-1-1 UFC) won for the fifth straight time and won by knockout for the first time since February 2010. Benavidez (19-4 MMA, 6-2 UFC) had a three-fight winning streak snapped.

As the UFC 189 tour made its last stop in Dublin, featherweight champ Jose Aldo was met with a torrent of abuse from the Irish fans. It might have been unpleasant, but it might also have been just what he needed.